\documentclass[a5paper,twoside,12pt]{book}
\input{preamble}
\setsansfont{Sanskrit 2003:script=deva}
\begin{document}
\input{frontmatter}
%\large
\Large
\setmainfont{Sanskrit 2003:script=deva}

\renewcommand{\partname}{विभागः}
\renewcommand{\thepart}{{\dndigit{\arabic{part}}}}

\input{stotras}
\newpage\mbox{}
\clearemptydoublepage
\mbox{}\clearemptydoublepage
\end{document}